There's lots of great swimming areas here, some are well known (Sliding Rock, French Broad) and many are off grid. Every one, except for the FB on occasion have been clean and we've had no issues with illness. Avoid Ledges River Park near Alexander (FB north of AVL) as it's been the dirtiest place we visited so far in the area.
Lake Lure and surrounding are actually nice places to spend the day. Although the lake is man made (1925), the Broad River flows through it so we're ok with it. The drive in, out and around the lake is pretty curvy, but not too bad. Come in from 64 during apple season and visit Stepp's
(LINK) while there to have a fun side trip while visiting the lake.
We're water people ourselves (our dog even more so) and find new favorites every week. Many of them we've had practically all to ourselves.